U.S. patent application number 09/927304 was filed with the patent office on 2003-02-13 for dielectric etch plasma chamber utilizing a magnetic filter to optimize plasma characteristics.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Trow, John R..
Application Number | 20030029837 09/927304 |
Document ID | / |
Family ID | 25454544 |
Filed Date | 2003-02-13 |
United States Patent
Application |
20030029837 |
Kind Code |
A1 |
Trow, John R. |
February 13, 2003 |
Dielectric etch plasma chamber utilizing a magnetic filter to
optimize plasma characteristics
Abstract
A method and a system for etching a substrate are disclosed. The
substrate is disposed in a process chamber. A flow of precursor gas
is introduced into the process chamber. An ionic plasma is then
formed from the precursor gas in a plasma volume within the process
chamber. A magnetic field is generated in the process chamber using
magnetic sources disposed external to the plasma volume. The
magnetic field divides the ionic plasma into a two regions, plasma
within one region having a higher electron temperature than plasma
within the other region. The low-electron temperature region is
confined substantially above the substrate. Radicals are formed in
this region for etching the substrate.
Inventors: |
Trow, John R.; (San Jose,
CA) |
Correspondence
Address: |
APPLIED MATERIALS, INC.
2881 SCOTT BLVD. M/S 2061
SANTA CLARA
CA
95050
US
|
Assignee: |
Applied Materials, Inc.
|
Family ID: |
25454544 |
Appl. No.: |
09/927304 |
Filed: |
August 10, 2001 |
Current U.S.
Class: |
216/67 ; 216/79;
216/80; 257/E21.252; 438/723; 438/732 |
Current CPC
Class: |
H01L 21/31116 20130101;
H01J 37/3266 20130101; H01J 37/32623 20130101; H01J 37/32082
20130101 |
Class at
Publication: |
216/67 ; 216/79;
216/80; 438/723; 438/732 |
International
Class: |
H01L 021/3065 |
Claims
What is claimed is:
1. A method for etching a substrate, the method comprising:
disposing the substrate in a process chamber; providing a flow of
precursor gas into the process chamber; forming an ionic plasma
from the precursor gas in a plasma volume within the process
chamber; generating a magnetic field in said process chamber using
magnetic sources disposed external to said plasma volume, wherein
said magnetic field divides said ionic plasma into a first region
and a second region, the second region confined substantially above
the substrate, plasma within the first region having a higher
electron temperature than plasma within the second region; and
forming radicals from plasma within the second region above said
substrate for etching said substrate.
2. The method recited in claim 1 wherein the ionic plasma is a
negative-ion plasma.
3. The method recited in claim 1 wherein the substrate comprises a
silicon oxide layer.
4. The method recited in claim 1 wherein forming the ionic plasma
from the precursor gas comprises ionizing the precursor gas using a
radio-frequency source.
5. The method recited in claim 4 wherein the precursor gas
comprises freon molecules.
6. The method recited in claim 5 wherein the precursor gas further
comprises argon.
7. The method recited in claim 5 wherein the precursor gas
comprises C.sub.4F.sub.8 molecules and forming radicals from plasma
within the second region comprises dissociating the C.sub.4F.sub.8
molecules into radical species including CF.sub.2.
8. The method recited in claim 5 wherein the precursor gas
comprises C.sub.4F.sub.8 molecules and forming radicals from plasma
within the second region comprises dissociating the C.sub.4F.sub.8
molecules into radical species including CF.sub.3.
9. The method recited in claim 1 wherein the magnetic sources
comprise permanent magnets.
10. The method recited in claim 1 wherein the magnetic sources
comprise electromagnets.
11. The method recited in claim 1 wherein the radicals are neutral
radicals.
12. A substrate processing system comprising: a housing defining a
process chamber; an ionic-plasma generating system operatively
coupled to the process chamber; a substrate holder configured to
hold a substrate during substrate processing; a gas-delivery system
configured to introduce gas into the process chamber; a
pressure-control system for maintaining a selected pressure within
the process chamber; a controller for controlling the ionic-plasma
generating system, the gas-delivery system, and the
pressure-control system to form an ionic plasma within the process
chamber; and a magnetic source disposed outside the process chamber
for generating a magnetic field, wherein the magnetic field divides
the ionic plasma into a first region and a second region, plasma
within the first region having a higher electron temperature than
plasma within the second region such that plasma within the second
region is confined substantially above the substrate to form
radicals for etching the substrate.
13. The substrate processing system recited in claim 12 wherein the
ionic plasma is a negative-ion plasma.
14. The substrate processing system recited in claim 12 wherein the
gas comprises freon molecules.
15. The substrate processing system recited in claim 14 wherein the
gas further comprises argon.
16. The substrate processing system recited in claim 14 wherein the
freon molecules comprise C.sub.4F.sub.8 molecules and the radicals
comprise CF.sub.2 radicals.
17. The substrate processing system recited in claim 14 wherein the
freon molecules comprise C.sub.4F.sub.8 molecules and the radicals
comprise CF.sub.3 radicals.
18. The substrate processing system recited in claim 12 wherein the
ionic-plasma generating system comprises radio-frequency coils.
19. The substrate processing system recited in claim 12 wherein the
magnetic source comprises a permanent magnet.
20. The substrate processing system recited in claim 12 wherein the
magnetic source comprises an electromagnet.
21. The substrate processing system recited in claim 12 wherein the
substrate comprises a dielectric material.
22. The substrate processing system recited in claim 21 wherein the
dielectric material comprises silicon oxide.
23. The substrate processing system recited in claim 12 wherein
electrons in the plasma within the second region have an energy
between approximately 1 and 300 eV.
Description
BACKGROUND OF THE INVENTION
[0001] The increasing complexity and miniaturization of integrated
circuit technology is driving the semiconductor industry. The
demand for improved resolution requires imaging features with
increasingly higher aspect ratios and smaller linewidth variation
over steep substrate topography. The semiconductor industry is
increasingly employing medium and high density reactors such as
inductively coupled plasma (ICP) systems as well as magnetron and
helicon plasmas. These technologies offer the ability for higher
rates and control of the ion energy for selectivity.
[0002] In high density reactive ion etching (RIE) systems its has
been found that electrons diffuse nearly isotropically from the
plasma source towards the wafer when the bias voltage is near its
maximum (Keller et al, Jpn. J. Appl. Phys. Vol. 38 (1999) pp.
4280-4282). One approach for decreasing the bias voltage in RF
systems involves applying a magnetic field to the plasma. The
magnetic field confines the electrons to the region near the
surface of the wafer and increases the ion flux density and ion
current. In this way, the voltage and ion energy requirements are
reduced. In a nonmagnetic RIE process for etching silicon dioxide
an RF energy at 13.56 MHz is applied to a system of 10-15 liters
volume, 50 millitorr pressure and an anode area to wafer-support
cathode area ratio of approximately (8-10) to 1, and develop wafer
(cathode) sheath voltage of approximately 800 volts. The
application of a magnetic field of 60 gauss allows a decrease of
25-30 percent of the bias voltage while allowing an increase in the
etch rate by approximately 50 percent.
[0003] The intent for using magnetic fields has previously been for
control of the electron energy for enhancing the production of
negative ion species, such as H.sup.- ions, which are only weakly
bound by about 0.75 eV. It is, however, desirable to provide a
system not only for controlling the energy and flux of the plasma
electrons and ions but also to enhance the chemical radical
formation at the surface of the wafer.
SUMMARY OF THE INVENTION
[0004] Thus, embodiments of the present invention provide a method
for etching a substrate. The substrate is disposed in a process
chamber, which is provided with a flow of precursor gas. An ionic
plasma is formed from the precursor gas in a plasma volume within
the process chamber. In one embodiment, the ionic plasma is a
negative-ion plasma. A magnetic field is generated within the
process chamber using magnetic sources disposed external to the
plasma volume such that the magnetic field divides the ionic plasma
into two regions. Plasma within the first region has a higher
electron temperature than plasma within the second region, which is
confined substantially above the substrate. Radicals are formed
from the plasma within the second region to etch the substrate.
[0005] In one embodiment the substrate comprises a silicon oxide
layer. The ionic plasma may be formed by ionizing the precursor gas
using a radio-frequency source. In a particular embodiment, the
precursor gas comprises freon molecules and may comprise a mixture
of argon and freon. The radicals formed in the second region may
thus be formed by dissociating C.sub.4F.sub.8 molecules into
radical species that include CF.sub.2 or include CF.sub.3. The
magnetic sources may be provided by permanent magnets or may be
provided by electromagnets in different embodiments.
[0006] The methods of the present invention may be performed with a
substrate processing system. Such a system may include a process
chamber, a plasma generation system, a substrate holder, a gas
delivery system, and a system controller. The magnetic sources are
disposed outside the process chamber to provide a magnetic field
for dividing the ionic plasma into two regions, including a
low-electron-temperature region confined substantially above the
substrate for forming radicals to etch the substrate.
[0007] A further understanding of the nature and advantages of the
present invention may be realized by reference to the remaining
portions of the specification and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 shows the electron interaction cross sections for
C.sub.3F.sub.8 provided by NIST;
[0009] FIG. 2 is a cross-sectional view of the plasma etch reactor
of the invention showing the disposition of the plasma source, the
disposition of the substrate and various elements and the shapes of
the magnetic field lines within the chamber;
[0010] FIG. 3 is a schematic process for formation of radicals on
the surface of the dielectric substrate;
[0011] FIG. 4 is a flow chart showing the method steps for etching
a substrate according to the present invention;
[0012] FIG. 5A illustrates one embodiment of a plasma etching
system according to the present inevntion;
[0013] FIG. 5B is a simplified, partial cross-sectional view of
processing chamber showing additional details of gas ring
inlet;
[0014] FIG. 5C is an illustration of a portion of an exemplary
system user interface used in conjunction with the exemplary plasma
processing chamber of FIG. 5A; and
[0015] FIG. 5D is an illustrative block diagram of the hierarchical
control structure of computer program controlling the plasma
processing sequence according to the present invention.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
[0016] Overview
[0017] Magnetic-filter embodiments of the invention provide a
method and apparatus for enhancing dielectric etch by increasing
the yield of chemical radical formation. This is achieved by
disposing a dielectric substrate in a plasma chamber. An ionic
plasma, such as a negative-ion plasma, is then formed in the plasma
chamber from a precursor gas. In addition to ionic species, the
plasma comprises electrons. In one embodiment, the precursor gas
comprises C.sub.4F.sub.8, and mad additionally comprise argon. A
magnetic field is then generated in the plasma chamber using
magnetic sources disposed external to the plasma volume where the
plasma is formed. The magnetic field is configured in such a manner
as to divide the ionic plasma into two regions. The plasma in the
first region has a higher electron temperature and the plasma in
the second region has a lower electron temperature. In this way,
the cooler plasma of the second region is confined above the
substrate intended for processing. Subsequently, radicals are
formed from the plasma in the second region above the substrate for
etching the dielectric substrate, which in one embodiment is
silicon oxide.
[0018] In one embodiment, the ionic plasma is created using a
radio-frequency (RF) source or microwave power source. The
frequency for generating RF energy may be within the range 100 kHz
to 100 MHz. The RF energy may be controlled by a tunable antenna.
In one embodiment, the tuning process is controlled by a variable
capacitance electrically connected between one end of the antenna
and RF ground.
[0019] In one embodiment, the magnetic field in the plasma chamber
is generated using a series of permanent magnets or using an
electromagnetic arrangement, such as may be provided with a set of
DC coils disposed around the plasma chamber, to apply a controlled
static magnetic field. In addition, magnetic sources may be mounted
around the plasma chamber for applying a multipolar cusp field to
the chamber in the vicinity of the substrate. This acts to confine
the high-energy plasma away from the substrate region while
substantially eliminating the magnetic field across the substrate.
The effect of this magnetic field is to act as a magnetic filter
that divides the plasma into the high-electron-temperatur- e and
low-electron-temperature regions as described above. Radicals are
formed in the second (low-electron-temperature) region via electron
attachment followed by dissociative processes.
[0020] Etchant Radical Formation Mechanism
[0021] Dissociative electron-molecule collisions play a key role in
a variety of plasma processes such as plasma-enhanced chemical
vapor deposition and low-temperature plasma etching.
Electron-molecule dissociation cross sections are relatively
difficult to measure because of well-known problems with the
detection of neutral fragments. Indeed, the number of systems for
which experimental measurements have been made is quite small. In
cases where electron-impact dissociation produces electronically
excited fragments decaying radiatively, studies use the optical
excitation function technique. Emissions have been measured over a
wide spectral range. Several molecules relevant to plasma
processing have been studied, providing dissociation cross sections
for CF.sub.4, SF.sub.6, NF.sub.3, BCl.sub.3 (A. Blanks, A. E.
Tabor, and K. Becker, J. Chem. Phys. 86:4871 (1987) and P. G.
Gilbert, R. B. Siegel, and K. Becker, Phys. Rev. A 41:5594 (1990))
and several freons (L. G. Christophorou and J. K. Olhoff, Electron
Interactions with C.sub.3F.sub.8, J. Phys. Chem. Ref Data, 27, No.
5, pp. 889-913 (1998)). "Freon" refers generally to fluorocarbon
compounds, including C.sub.3F.sub.8 and C.sub.4F.sub.8. Data on
electron-molecule collisional processes provides the identities of
key chemical species and the dominant kinetic pathways that
determine the concentrations and reactivities of these key species.
In some cases, numerous dissociative channels leading to various
products are possible in electron-molecule collision, especially
when the molecule presents a large number of atoms, such as in
freon molecules.
[0022] The advantage of controlling the energy of the electrons by
using the magnetic filter discussed previously is that it is then
possible to enhance chemical radical formation without
over-dissociating the precursor gas. Radical species formed above
the substrate may then be used to etch the substrate. In one
embodiment, the precursor gas is a mixture of a freon and an inert
gas such as argon. In a particular embodiment, the freon is
C.sub.4F.sub.8. According to embodiments of the present invention,
it is possible not only to control the formation of ions but also
to control the fluorine chemistry used for oxide etch. Indeed, such
embodiments permit an increase in the yield of radical formation of
CF.sub.3 and CF.sub.2 species while limiting the formation of other
radical or ionic species. In addition to CF.sub.3 and CF.sub.2
radicals, formation of other radicals in the
electron-C.sub.4F.sub.8 collision is possible. It has been shown,
for perfluoropropane C.sub.3F.sub.8, that dissociative processes
occur within the electron energy interval of 1 eV to 300 eV (see
the discussion related to FIG. 1 below). Complete cross-section
measurements for C.sub.4F.sub.8 appear to be unavailable. However,
relevant reaction information is provided by C.sub.3F.sub.8
cross-section data. Indeed, it is evident from such cross-section
results that higher radical yield is achieved by maintaining a low
collisional energy between the electrons in the plasma and the
precursor gas.
[0023] FIG. 1 shows the electron interaction cross sections for the
C.sub.3F.sub.8 molecule. The electron energy represents the energy
of the incident electron in units of electron volts. The curve
labeled "Total Scattering" represents the total electron scattering
cross section in units of 10.sup.-20 m.sup.2. The curve labeled
"Elastic Integral" represents the integral elastic electron
scattering cross section in units of 10.sup.-20 m.sup.2. The curve
labeled "Momentum Transfer" represents the elastic momentum
transfer cross section in units of 10.sup.-20 m.sup.2. The curve
labeled "Total Ionization" represents the total electron-impact
ionization cross section in units of 10.sup.-20 m.sup.2. The curve
labeled "Total Dissociation" represents the total electron-impact
dissociation cross section in units of 10.sup.-20 m.sup.2. The
curve labeled "Total Attachment" represents the total
electron-attachment cross section in units of 10.sup.-20 m.sup.2.
In particular, it represents the sum of cross sections for
attachment processes producing parent negative ions and fragment
negative ions. The curve labeled "Dissociative Attachment"
represents the dissociative electron-attachment cross section in
units of 10.sup.-20 m.sup.2. It represents the cross section only
for processes producing fragment negative ions.
[0024] The data presented on FIG. 1 offer insight as to which
process is predominant at certain electron collision energies. In
particular, it may be seen that the dissociative attachment, that
is a dissociation channel with one of the products of the collision
being ionic, appears between approximately 1 eV and 8 eV. However,
the cross section of the dissociative attachment channel is two
order of magnitude lower than the total scattering cross section,
meaning that this process is negligible in comparison with other
processes such as elastic and momentum transfer collisions. In
comparison, the total dissociation cross-section leading to radical
species (neutral molecules) becomes important at around 10 eV and
stays at a value of approximately 10.times.10.sup.-20 m.sup.2 up to
an electron energy of about 300 eV. In the electron energy range
20-100 eV the total dissociation and the total ionization channels
have approximately equal cross section values meaning that in this
interval of energy the probability of producing ions or radicals is
about the same. Therefore, a compromise may be negotiated in terms
of the electron energy to dissociate the parent molecule
C.sub.3F.sub.8 to produce radicals without over-dissociating the
freon molecule.
[0025] The mechanism of the invention may be better understood with
reference to FIG. 2, in which a schematic cross-sectional view of a
plasma etch reactor 200 that may be used with the invention is
shown. A plasma generator 201, such as an RF source, is mounted on
top of the plasma processing chamber 202. A gas source 209 provides
a plasma process gas through inlet 210. An exhaust pump (not shown
in FIG. 2) withdraws process gases and reaction by-products at a
rate sufficient to produce an appropriate pressure within
processing chamber 202.
[0026] A series of DC coils 203, 204, 205 are disposed around
plasma chamber 202 in order to create the magnetic field
represented by magnetic field lines 206. The magnetic field lines
206 confine high-temperature-electron plasma 207 away from the
substrate 208. Indeed, due to the Lorentz relationship F=q
(v.times.B), which provides the force F on particles of charge q
traveling at velocity v in field B, the high-energy electrons in
the plasma are bent back or repelled by the magnetic field and are
not able to penetrate to the substrate processing region 215.
Therefore, the presence of high-energy electrons is substantially
reduced in the processing region 215. The processing region 215 is
instead populated with lower-temperature electrons to provide a
better scheme for chemical radical production. Indeed, as mentioned
previously, dissociative attachment processes occur, preferably, at
low electron collision energy. The approach using a magnetic filter
disposed outside the plasma offers the advantage of enhancing the
etch process by increasing the yield of radical species
formation.
[0027] Referring to FIG. 3, a process is shown schematically for
formation of radicals on the surface of the dielectric substrate
when etching of silicon oxide layers with fluorine-based etchant
molecules is desired. Low-energy electrons 301 present in the
low-temperature plasma 215 collide with freon C.sub.4F.sub.8
molecules 302, leading to formation of radical species 303 and 304.
In one embodiment, these radical species are respectively CF.sub.2
and CF.sub.3 molecules. Radicals 303 and 304 etch the dielectric
substrate 208, which may comprise a layer of silicon oxide. To
produce a structure for etching, photoresist mask 305 is used to
protect those portions of the silicon oxide layer not intended for
etching.
[0028] FIG. 4 is an exemplary flow chart showing the method steps
for etching a substrate according to the present invention. The
illustrated method begins at block 401 by disposing the substrate
in a process chamber. At block 402 a flow of process precursor gas
is provided into the chamber. At block 403 a negative-ion plasma is
formed from the precursor gas in a plasma volume within the process
chamber. At block 404 a magnetic field is generated in the process
chamber using magnetic sources disposed external to the plasma
volume. At block 405 the negative-ion plasma is divided with the
magnetic field into a first region 406 and a second region 407,
plasma in the first region 406 having a higher electron temperature
than plasma within the second region 407. The second region 407 is
confined substantially above the substrate. Radicals are formed at
block 408 from the plasma region 407 for etching the substrate.
[0029] Exemplary Substrate Processing System
[0030] The following is a description of a plasma processing
chamber that may be used for practicing embodiments of the present
invention. FIG. 5A illustrates one embodiment of a plasma etching
system 10 in which a dielectric according to the present invention
can be etched. System 10 includes a chamber 13, a vacuum system 70,
a source plasma system 80A, a bias plasma system 80B, a gas
delivery system 33, and a remote plasma cleaning system 50.
[0031] The upper portion of chamber 13 includes a dome 14, which is
made of a ceramic dielectric material, such as aluminum oxide or
aluminum nitride. Dome 14 defines an upper boundary of a plasma
processing region 16. Plasma processing region 16 is bounded on the
bottom by the upper surface of a substrate 17 and a substrate
support member 18.
[0032] A heater plate 23 and a cold plate 24 surmount, and are
thermally coupled to, dome 14. Heater plate 23 and cold plate 24
allow control of the dome temperature to within about
.+-.10.degree. C. over a range of about 100.degree. C. to
200.degree. C. This allows optimizing the dome temperature for the
various processes. For example, it may be desirable to maintain the
dome at a higher temperature for etching (or cleaning) processes
than would be desirable for deposition processes.
[0033] The lower portion of chamber 13 includes a body member 22,
which joins the chamber to the vacuum system. A base portion 21 of
substrate support member 18 is mounted on, and forms a continuous
inner surface with, body member 22. Substrates are transferred into
and out of chamber 13 by a robot blade (not shown) through an
insertion/removal opening (not shown) in the side of chamber 13.
Lift pins (not shown) are raised and then lowered under the control
of a motor (also not shown) to move the substrate from the robot
blade at an upper loading position 57 to a lower processing
position 56 in which the substrate is placed on a substrate
receiving portion 19 of substrate support member 18. Substrate
receiving portion 19 includes an electrostatic chuck 20 that
secures the substrate to substrate support member 18 during
substrate processing. In a preferred embodiment, substrate support
member 18 is made from an aluminum oxide or aluminum ceramic
material.
[0034] Vacuum system 70 includes throttle body 25, which houses
twin-blade throttle valve 26 and is attached to gate valve 27 and
turbo-molecular pump 28. It should be noted that throttle body 25
offers minimum obstruction to gas flow, and allows symmetric
pumping. Gate valve 27 can isolate pump 28 from throttle body 25,
and can also control chamber pressure by restricting the exhaust
flow capacity when throttle valve 26 is fully open. The arrangement
of the throttle valve, gate valve, and turbo-molecular pump allow
accurate and stable control of chamber pressures from between about
1 millitorr to about 2 torr.
[0035] The source plasma system 80A includes a top coil 29 and side
coil 30, mounted on dome 14. A symmetrical ground shield (not
shown) reduces electrical coupling between the coils. Top coil 29
is powered by top source RF (SRF) generator 31A, whereas side coil
30 is powered by side SRF generator 31B, allowing independent power
levels and frequencies of operation for each coil. This dual coil
system allows control of the radial ion density in chamber 13,
thereby improving plasma uniformity. Side coil 30 and top coil 29
are typically inductively driven, which does not require a
complimentary electrode. In a specific embodiment, the top source
RF generator 31A provides up to 2,500 watts of RF power at
nominally 2 MHz and the side source RF generator 31B provides up to
5,000 watts of RF power at nominally 2 MHz. The operating
frequencies of the top and side RF generators may be offset from
the nominal operating frequency (e.g. to 1.7-1.9 MHz and 1.9-2.1
MHz, respectively) to improve plasma-generation efficiency.
[0036] A bias plasma system 80B includes a bias RF ("BRF")
generator 31C and a bias matching network 32C. The bias plasma
system 80B capacitively couples substrate portion 17 to body member
22, which act as complimentary electrodes. The bias plasma system
80B serves to enhance the transport of plasma species (e.g., ions)
created by the source plasma system 80A to the surface of the
substrate. In a specific embodiment, bias RF generator provides up
to 5,000 watts of RF power at 13.56 MHz.
[0037] RF generators 31A and 31B include digitally controlled
synthesizers and operate over a frequency range between about 1.8
to about 2.1 MHz. Each generator includes an RF control circuit
(not shown) that measures reflected power from the chamber and coil
back to the generator and adjusts the frequency of operation to
obtain the lowest reflected power, as understood by a person of
ordinary skill in the art. RF generators are typically designed to
operate into a load with a characteristic impedance of 50 ohms. RF
power may be reflected from loads that have a different
characteristic impedance than the generator. This can reduce power
transferred to the load. Additionally, power reflected from the
load back to the generator may overload and damage the generator.
Because the impedance of a plasma may range from less than 5 ohms
to over 900 ohms, depending on the plasma ion density, among other
factors, and because reflected power may be a function of
frequency, adjusting the generator frequency according to the
reflected power increases the power transferred from the RF
generator to the plasma and protects the generator. Another way to
reduce reflected power and improve efficiency is with a matching
network.
[0038] Matching networks 32A and 32B match the output impedance of
generators 31A and 31B with their respective coils 29 and 30. The
RF control circuit may tune both matching networks by changing the
value of capacitors within the matching networks to match the
generator to the load as the load changes. The RF control circuit
may tune a matching network when the power reflected from the load
back to the generator exceeds a certain limit. One way to provide a
constant match, and effectively disable the RF control circuit from
tuning the matching network, is to set the reflected power limit
above any expected value of reflected power. This may help
stabilize a plasma under some conditions by holding the matching
network constant at its most recent condition. Other measures may
also help stabilize a plasma. For example, the RF control circuit
can be used to determine the power delivered to the load (plasma)
and may increase or decrease the generator output power to keep the
delivered power substantially constant during a process.
[0039] A gas delivery system 33 provides gases from several
sources, 34A-34F chamber for processing the substrate via gas
delivery lines 38 (only some of which are shown). As would be
understood by a person of skill in the art, the actual sources used
for sources 34A-34F and the actual connection of delivery lines 38
to chamber 13 varies depending on the etching and cleaning
processes executed within chamber 13. Gases are introduced into
chamber 13 through a gas ring 37 and/or a top nozzle 45. FIG. 5B is
a simplified, partial cross-sectional view of chamber 13 showing
additional details of gas ring 37.
[0040] In one embodiment, first and second gas sources, 34A and
34B, and first and second gas flow controllers, 35A' and 35B',
provide gas to ring plenum 36 in gas ring 37 via gas delivery lines
38 (only some of which are shown). Gas ring 37 has a plurality of
source gas nozzles 39 (only one of which is shown for purposes of
illustration) that provide a uniform flow of gas over the
substrate. Nozzle length and nozzle angle may be changed to allow
tailoring of the uniformity profile and gas utilization efficiency
for a particular process within an individual chamber. In a
preferred embodiment, gas ring 37 has 12 source gas nozzles made
from an aluminum oxide ceramic.
[0041] Gas ring 37 also has a plurality of oxidizer gas nozzles 40
(only one of which is shown), which in a preferred embodiment are
co-planar with and shorter than source gas nozzles 39, and in one
embodiment receive gas from body plenum 41. In some embodiments it
is desirable not to mix source gases and oxidizer gases before
injecting the gases into chamber 13. In other embodiments, oxidizer
gas and source gas may be mixed prior to injecting the gases into
chamber 13 by providing apertures (not shown) between body plenum
41 and gas ring plenum 36. In one embodiment, third and fourth gas
sources, 34C and 34D, and third and fourth gas flow controllers,
35C and 35D', provide gas to body plenum via gas delivery lines 38.
Additional valves, such as 43B (other valves not shown), may shut
off gas from the flow controllers to the chamber.
[0042] In embodiments where flammable, toxic, or corrosive gases
are used, it may be desirable to eliminate gas remaining in the gas
delivery lines after a process. This may be accomplished using a
3-way valve, such as valve 43B, to isolate chamber 13 from delivery
line 38A and to vent delivery line 38A to vacuum foreline 44, for
example. As shown in FIG. 1A, other similar valves, such as 43A and
43C, may be incorporated on other gas delivery lines. Such 3-way
valves may be placed as close to chamber 13 as practical, to
minimize the volume of the unvented gas delivery line (between the
3-way valve and the chamber). Additionally, two-way (on-off) valves
(not shown) may be placed between a mass flow controller ("MFC")
and the chamber or between a gas source and an MFC.
[0043] Referring again to FIG. 5A, chamber 13 also has top nozzle
45 and top vent 46. Top nozzle 45 and top vent 46 allow independent
control of top and side flows of the gases, which improves gas flow
uniformity and allows fine adjustment of the film's etching
parameters. Top vent 46 is an annular opening around top nozzle 45.
In one embodiment, first gas source 34A supplies source gas nozzles
39 and top nozzle 45. Source nozzle MFC 35A' controls the amount of
gas delivered to source gas nozzles 39 and top nozzle MFC 35A
controls the amount of gas delivered to top gas nozzle 45.
Similarly, two MFCs 35B and 35B' may be used to control the flow of
oxygen to both top vent 46 and oxidizer gas nozzles 40 from a
single source of oxygen, such as source 34B. The gases supplied to
top nozzle 45 and top vent 46 may be kept separate prior to flowing
the gases into chamber 13, or the gases may be mixed in top plenum
48 before they flow into chamber 13. Separate sources of the same
gas may be used to supply various portions of the chamber.
[0044] A remote microwave-generated plasma cleaning system 50 is
provided to periodically clean residues from chamber components.
The cleaning system includes a remote microwave generator 51 that
creates a plasma from a cleaning gas source 34E (e.g., molecular
fluorine, nitrogen trifluoride, other fluorocarbons or equivalents)
in reactor cavity 53. The reactive species resulting from this
plasma are conveyed to chamber 13 through cleaning gas feed port 54
via applicator tube 55. The materials used to contain the cleaning
plasma (e.g., cavity 53 and applicator tube 55) must be resistant
to attack by the plasma. The distance between reactor cavity 53 and
feed port 54 should be kept as short as practical, since the
concentration of desirable plasma species may decline with distance
from reactor cavity 53. Generating the cleaning plasma in a remote
cavity allows the use of an efficient microwave generator and does
not subject chamber components to the temperature, radiation, or
bombardment of the glow discharge that may be present in a plasma
formed in situ. Consequently, relatively sensitive components, such
as electrostatic chuck 20, do not need to be covered with a dummy
substrate or otherwise protected, as may be required with an in
situ plasma cleaning process. In one embodiment, this cleaning
system is used to dissociate atoms of the etchant gas remotely,
which are then supplied to the process chamber 13. In another
embodiment, the etchant gas is provided directly to the process
chamber 13. In still a further embodiment, multiple process
chambers are used, with deposition and etching steps being
performed in separate chambers.
[0045] System controller 60 controls the operation of system 10. In
a preferred embodiment, controller 60 includes a memory 62, such as
a hard disk drive, a floppy disk drive (not shown), and a card rack
(not shown) coupled to a processor 61. The card rack may contain a
single-board computer (SBC) (not shown), analog and digital
input/output boards (not shown), interface boards (not shown), and
stepper motor controller boards (not shown). The system controller
conforms to the Versa Modular European ("VME") standard, which
defines board, card cage, and connector dimensions and types. The
VME standard also defines the bus structure as having a 16 bit data
bus and 24-bit address bus. System controller 31 operates under the
control of a computer program stored on the hard disk drive or
through other computer programs, such as programs stored on a
removable disk. The computer program dictates, for example, the
timing, mixture of gases, RF power levels and other parameters of a
particular process. The interface between a user and the system
controller is via a monitor, such as a cathode ray tube ("CRT") 65,
and a light pen 66, as depicted in FIG. 5C.
[0046] FIG. 5C is an illustration of a portion of an exemplary
system user interface used in conjunction with the exemplary plasma
processing chamber of FIG. 5A. System controller 60 includes a
processor 61 coupled to a computer-readable memory 62. Preferably,
memory 62 may be a hard disk drive, but memory 62 may be other
kinds of memory, such as ROM, PROM, and others.
[0047] System controller 60 operates under the control of a
computer program 63 stored in a computer-readable format within
memory 62. The computer program dictates the timing, temperatures,
gas flows, RF power levels and other parameters of a particular
process. The interface between a user and the system controller is
via a CRT monitor 65 and a light pen 66, as depicted in FIG. 5C. In
a preferred embodiment, two monitors, 65 and 65A, and two light
pens, 66 and 66A, are used, one mounted in the clean room wall (65)
for the operators and the other behind the wall (65A) for the
service technicians. Both monitors simultaneously display the same
information, but only one light pen (e.g. 66) is enabled. To select
a particular screen or function, the operator touches an area of
the display screen and pushes a button (not shown) on the pen. The
touched area confirms being selected by the light pen by changing
its color or displaying a new menu, for example.
[0048] The computer program code can be written in any conventional
computer-readable programming language such as 68000 assembly
language, C, C++, or Pascal. Suitable program code is entered into
a single file, or multiple files, using a conventional text editor
and is stored or embodied in a computer-usable medium, such as a
memory system of the computer. If the entered code text is in a
high level language, the code is compiled, and the resultant
compiler code is then linked with an object code of precompiled
windows library routines. To execute the linked compiled object
code, the system user invokes the object code causing the computer
system to load the code in memory. The CPU reads the code from
memory and executes the code to perform the tasks identified in the
program.
[0049] FIG. 5D shows an illustrative block diagram of the
hierarchical control structure of computer program 500. A user
enters a process set number and process chamber number into a
process selector subroutine 510 in response to menus or screens
displayed on the CRT monitor by using the light pen interface. The
process sets are predetermined sets of process parameters necessary
to carry out specified processes, and are identified by predefined
set numbers. Process selector subroutine 510 identifies (i) the
desired process chamber in a multichamber system, and (ii) the
desired set of process parameters needed to operate the process
chamber for performing the desired process. The process parameters
for performing a specific process relate to conditions such as
process gas composition and flow rates, temperature, pressure,
plasma conditions such as RF power levels, and chamber dome
temperature, and are provided to the user in the form of a recipe.
The parameters specified by the recipe are entered utilizing the
light pen/CRT monitor interface.
[0050] The signals for monitoring the process are provided by the
analog and digital input boards of system controller 60, and the
signals for controlling the process are output on the analog and
digital output boards of system controller 60.
[0051] A process sequencer subroutine 520 comprises program code
for accepting the identified process chamber and set of process
parameters from the process selector subroutine 510 and for
controlling operation of the various process chambers. Multiple
users can enter process set numbers and process chamber numbers, or
a single user can enter multiple process set numbers and process
chamber numbers; sequencer subroutine 520 schedules the selected
processes in the desired sequence. Preferably, sequencer subroutine
520 includes a program code to perform the steps of (i) monitoring
the operation of the process chambers to determine if the chambers
are being used, (ii) determining what processes are being carried
out in the chambers being used, and (iii) executing the desired
process based on availability of a process chamber and type of
process to be carried out. Conventional methods of monitoring the
process chambers can be used, such as polling. When scheduling
which process is to be executed, sequencer subroutine 520 can be
designed to take into consideration the "age" of each particular
user-entered request, or the present condition of the process
chamber being used in comparison with the desired process
conditions for a selected process, or any other relevant factor a
system programmer desires to include for determining scheduling
priorities.
[0052] After sequencer subroutine 520 determines which process
chamber and process set combination is going to be executed next,
sequencer subroutine 520 initiates execution of the process set by
passing the particular process set parameters to a chamber manager
subroutine 530A-C, which controls multiple processing tasks in
chamber 13 and possibly other chambers (not shown) according to the
process set sent by sequencer subroutine 520.
[0053] Examples of chamber component subroutines are substrate
positioning subroutine 540, process gas control subroutine 550,
pressure control subroutine 560, and plasma control subroutine 570.
Those having ordinary skill in the art will recognize that other
chamber control subroutines can be included depending on what
processes are selected to be performed in chamber 13. In operation,
chamber manager subroutine 530A selectively schedules or calls the
process component subroutines in accordance with the particular
process set being executed. Chamber manager subroutine 530A
schedules process component subroutines in the same manner that
sequencer subroutine 520 schedules the process chamber and process
set to execute. Typically, chamber manager subroutine 530A includes
steps of monitoring the various chamber components, determining
which components need to be operated based on the process
parameters for the process set to be executed, and causing
execution of a chamber component subroutine responsive to the
monitoring and determining steps.
[0054] Operation of particular chamber component subroutines will
now be described with reference to FIGS. 5A and 5D. Substrate
positioning subroutine 540 comprises program code for controlling
chamber components that are used to load a substrate onto substrate
support number 18. Substrate positioning subroutine 540 may also
control transfer of a substrate into chamber 13 from, e.g., another
reactor in the multi-chamber system, after other processing has
been completed.
[0055] Process gas control subroutine 550 has program code for
controlling process gas composition and flow rates. Subroutine 550
controls the open/close position of the safety shut-off valves and
also ramps up/ramps down the mass flow controllers to obtain the
desired gas flow rates. All chamber component subroutines,
including process gas control subroutine 550, are invoked by
chamber manager subroutine 530A. Subroutine 550 receives process
parameters from chamber manager subroutine 530A related to the
desired gas flow rates.
[0056] Typically, process gas control subroutine 550 opens the gas
supply lines, and repeatedly (i) reads the necessary mass flow
controllers, (ii) compares the readings to the desired flow rates
received from chamber manager subroutine 530A, and (iii) adjusts
the flow rates of the gas supply lines as necessary. Furthermore,
process gas control subroutine 550 may include steps for monitoring
the gas flow rates for unsafe rates and for activating the safety
shut-off valves when an unsafe condition is detected.
[0057] In some processes, an inert gas, such as argon, is flowed
into chamber 13 to stabilize the pressure in the chamber before
reactive process gases are introduced. For these processes, the
process gas control subroutine 550 is programmed to include steps
for flowing the inert gas into chamber 13 for an amount of time
necessary to stabilize the pressure in the chamber. The steps
described above may then be carried out.
[0058] Additionally, when a process gas is to be vaporized from a
liquid precursor, for example, tetraethylorthosilane (TEOS), the
process gas control subroutine 550 may include steps for bubbling a
delivery gas such as helium through the liquid precursor in a
bubbler assembly or for introducing the helium to a liquid
injection valve. For this type of process, the process gas control
subroutine 550 regulates the flow of the delivery gas, the pressure
in the bubbler, and the bubbler temperature to obtain the desired
process gas flow rates. As discussed above, the desired process gas
flow rates are transferred to process gas control subroutine 550 as
process parameters.
[0059] Furthermore, the process gas control subroutine 550 includes
steps for obtaining the necessary delivery gas flow rate, bubbler
pressure, and bubbler temperature for the desired process gas flow
rate by accessing a stored table containing the necessary values
for a given process gas flow rate. Once the necessary values are
obtained, the delivery gas flow rate, bubbler pressure and bubbler
temperature are monitored, compared to the necessary values and
adjusted accordingly.
[0060] The process gas control subroutine 550 may also control the
flow of heat-transfer gas, such as helium (He), through the inner
and outer passages in the substrate chuck with an independent
helium control (IHC) subroutine (not shown). The gas flow thermally
couples the substrate to the chuck. In a typical process, the
substrate is heated by the plasma and the chemical reactions that
etch the layer, and the He cools the substrate through the chuck,
which may be water-cooled. This keeps the substrate below a
temperature that may damage preexisting features on the
substrate.
[0061] Pressure control subroutine 560 includes program code for
controlling the pressure in chamber 13 by regulating the size of
the opening of throttle valve 26 in the exhaust portion of the
chamber. There are at least two basic methods of controlling the
chamber with the throttle valve. The first method relies on
characterizing the chamber pressure as it relates to, among other
things, the total process gas flow, the size of the process
chamber, and the pumping capacity. The first method sets throttle
valve 26 to a fixed position. Setting throttle valve 26 to a fixed
position may eventually result in a steady-state pressure.
[0062] Alternatively, the chamber pressure may be measured, with a
manometer for example, and the position of throttle valve 26 may be
adjusted according to pressure control subroutine 560, assuming the
control point is within the boundaries set by gas flows and exhaust
capacity. The former method may result in quicker chamber pressure
changes, as the measurements, comparisons, and calculations
associated with the latter method are not invoked. The former
method may be desirable where precise control of the chamber
pressure is not required, whereas the latter method may be
desirable where an accurate, repeatable, and stable pressure is
desired.
[0063] When pressure control subroutine 560 is invoked, the
desired, or target, pressure level is received as a parameter from
chamber manager subroutine 530A. Pressure control subroutine 560
measures the pressure in chamber 13 by reading one or more
conventional pressure manometers connected to the chamber; compares
the measured value(s) to the target pressure; obtains proportional,
integral, and differential (PID) values from a stored pressure
table corresponding to the target pressure, and adjusts throttle
valve 26 according to the PID values obtained from the pressure
table. Alternatively, pressure control subroutine 160 may open or
close throttle valve 26 to a particular opening size to regulate
the pressure in chamber 13 to a desired pressure or pressure
range.
[0064] Plasma control subroutine 570 comprises program code for
controlling the frequency and power output setting of RF generators
31A and 31B and for tuning matching networks 32A and 32B. Plasma
control subroutine 570, like the previously described chamber
component subroutines, is invoked by chamber manager subroutine
530A.
[0065] An example of a system that may incorporate some or all of
the subsystems and routines described above would be the ULTIMA.TM.
system, manufactured by APPLIED MATERIALS, INC., of Santa Clara,
Calif., configured to practice the present invention. Further
details of such a system are disclosed in the commonly assigned
U.S. patent application Ser. No. 08/679,927, filed Jul. 15, 1996,
entitled "Symmetric Tunable Inductively-Coupled HDP-CVD Reactor,"
having Fred C. Redeker, Farhad Moghadam, Hirogi Hanawa, Tetsuya
Ishikawa, Dan Maydan, Shijian Li, Brian Lue, Robert Steger, Yaxin
Wang, Manus Wong and Ashok Sinha listed as co-inventors, the
disclosure of which is incorporated herein by reference. The
described system is for exemplary purpose only. It would be a
matter of routine skill for a person of skill in the art to select
an appropriate conventional substrate processing system and
computer control system to implement the present invention.
[0066] While a detailed description of presently preferred
embodiments of the invention have been given above, various
alternatives, modifications, and equivalents will be apparent to
those skilled in the art without varying from the spirit of the
invention. Therefore, the above description should not be taken as
limiting the scope of the invention, which is defined by the
appended claims.
* * * * *